Generally, it is known that asymmetrical C.sub.4 -C.sub.7 alkyl tertiary alkyl ethers are particularly useful as octane improvers for liquid fuels, especially gasoline. Methyl tertiary butyl ether (MTBE), ethyl t-butyl ether (ETBE), isopropyl t-butyl ether (IPTBE) and tertiary amyl methyl ether (TAME) are known to exhibit high octane properties. Much attention has been focused on production of these ethers due to the rapidly increasing demand for lead-free octane boosters for gasoline.
It is known in the art to produce MTBE or ETBE by reacting isobutylene with either methanol or ethanol, resulting in the formation or MTBE of ETBE, respectively. The reaction normally is conducted in liquid phase with relatively mild conditions. The isobutylene can be obtained from various sources, such as naphtha cracking, catalytic cracking, etc. The resulting reaction product stream contains the desired MTBE or ETBE, as well as unreacted isobutene and other C.sub.4 hydrocarbons and methanol or ethanol.
Since oxygenates are used as gasoline blending components, extenders, octane boosters and as key ingredients for reducing the emissions of CO and VOCs (Volatile Organic Compounds), it is expected that the demand for oxygenates will increase enormously in the coming years. See F. Cunill, et al., "Effect of Water Presence on Methyl tert-Butyl Ether and Ethyl tert-Butyl Ether Liquid-Phase Synthesis". Ind. Eng. Chem. Res. 1993, 32, 564-569.
Of all oxygenates, the tertiary ethers, such as methyl t-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME) are preferred by refineries to lighter alcohols. They have lower blending Ried vapor pressure (BRvp), lower vaporization latent heats and low solubilities in water. The most common ether in use today is MTBE with a projected production of about 25 million metric tons.
With the expanding use of MTBE as an acceptable gasoline additive, a growing problem is the availability of raw materials. As mentioned, the critical raw material is historically isobutylene (Oil and Gas J., Jun. 8, 1987, p. 55). A number of recent patents to Texaco Chemical Co., noted below, use t-butanol, rather than isobutylene, in a one step reaction.
The main drawback of tertiary ethers, is that they substantially increase aldehyde emissions, which are under EPA regulations and have to decrease 15% by 1995. It is believed this drawback could be largely circumvented by mixing the tertiary ethers with tertiary alcohols. Tertiary butyl alcohol (tBA) has a very low atmospheric reactivity and low aldehyde emissions, since no hydrogens are contained in the carbon link to the oxygen. Basis experience acquired with tBA during the 1970s, a gasoline blended with a mixture of ethers and tBA and/or tertiary amyl alcohol should be shippable, Ibid.
The use of zeolites for certain organic transformation reactions is known in the art. Beta-zeolite was first synthesized at Mobil R and D labs and exhibited improved thermal and acid stability over previously synthesized zeolites.
One of the earliest disclosures of .beta.-zeolite was in U.S. Pat. No. 3,308,069 (1967) to Wadinger et al.
J. B. Higgins, et al. of Mobil Research and Development published an article in Zeolites, 1988, Vol. 8, November, 446-452 titled "The Framework Topology of Zeolite Beta." In the article Higgins et al. disclose what is known about the framework topology of .beta.-zeolite. The information has been determined using a combination of model building, distance-least-square refinement and powder pattern simulation.
In an article titled "Cumene Disproportionation over Zeolite Beta I. Comparison of Catalytic Performances and Reaction Mechanisms of Zeolites," Applied Catalysis, 77 (1991) 199-207, Tseng-Chang Tsai, Chin-Lan Ay and Ikai Wang disclose a study demonstrating that cumene disproportionation can be applied as a probe reaction for zeolite structure. It is revealed that .beta.-zeolite would have application potential in the production of diisopropylbenzene for reasons of activity, selectivity and stability.
In a second part of the article by Tsai et al., "II. Stability Enhancement with Silica Deposition and Steam Pretreatment", Ibid, pp. 209-222, Tsai and Wang disclose their development of two methods to improve the stability of .beta.-zeolite, silica deposition and steam pretreatment.
E. Bourgeat-Lami et al. have published an article discussing their study on the effects of calcination of zeolite beta, as synthesized, or after ammonium-exchange. See "Stability of the Tetrahedral Aluminum Sites in Zeolite Beta," E. Bourgeat et al., Catalysis Letters, 1990, 5, 265. These researchers came to the conclusion that the tetrahedral aluminum sites disappearing upon calcination can be readily restored by a simple treatment in ammonium nitrate. The parent sample of .beta.-zeolite with a Si/Al ratio of 16.9 was synthesized at 130.degree. C. using tetraethylammonium hydroxide (TEA) as template. The NMR spectrum indicated a dealumination corresponding to about 25%. When this material was treated with ammonium nitrate solution, washed and over dried at 70.degree. C., the signal of octahedral aluminum was no longer detected while that at 53 ppm narrowed and increased to 95% of its original value.
An article titled "Beta-Zeolite as Catalyst or Catalyst Additive for the Production of Olefins During Cracking or Gas Oil," was written by L. Bonetto et al., 9th International Zeolite Conference, July 1992, FP 22. The authors note that with the greater demand for oxygenated compounds there is indication there might be increased demands for catalysts and conditions which maximize C.sub.3, C.sub.4 and C.sub.5 olefins. They suggest that .beta.-zeolite could be used alone or combined with Y-zeolite as a suitable zeolite component. Various catalysts were studied with respect to minimization of diffusional requirements and zeolite stability.
Japanese Patent 007432 teaches the use of zeolites to make dialkyl ethers containing primary or secondary alkyl groups.
U.S. Pat. No. 4,058,576 to Chang et al. teaches the use of (pentasil-type) aluminosilicate zeolites, such as ZSM-5, having a pore size greater than 5 angstrom units and a silica-to-alumina ratio of at least 12, to convert lower alcohols to a mixture of ethers and olefins.
U.S. Pat. No. 4,419,220, to Mobil, discloses a process for dewaxing a hydrocarbon feedstock containing straight chain paraffins which comprises contacting the feedstock with a .beta.-zeolite catalyst having a Si:Al ratio of at least 30:1 and a hydrogenation component under isomerization conditions.
Another European Application to Mobil, EPO 0 094 82, discloses simultaneous catalytic hydrocracking and hydrodewaxing of hydrocarbon oils with .beta.-zeolite.
In European Patent Application 0 095 303, to Mobil, there is a disclosure of dewaxing distillate fuel oils by the use of .beta.-zeolite catalysts which, preferably have a silica:alumina ratio over 100:1. Ratios as high as 250:1 and 500:1 are disclosed as useful.
Another U.S. Pat. No. 4,518,485, to Mobil, discloses a process for dewaxing a hydrocarbon feedstock containing paraffins selected from the group of normal paraffins and slightly branched paraffins and sulfur and nitrogen compounds where, after conventionally hydrotreating the feedstock to remove sulfur and nitrogen, the hydrotreated feedstock is dewaxed by contacting the feedstock with a catalyst comprising .beta.-zeolite having a silica/alumina ratio of at least 30:1.
In U.S. Pat. No. 4,740,292, to Mobil, there is disclosed a catalytic cracking process which comprises cracking a hydrocarbon feed in the absence of added hydrogen with a cracking catalyst comprising a .beta.-zeolite component and a faujasite component comprising at least one crystalline aluminosilicate of the faujasite structure, the weight ratio of the faujasite component to the .beta.-zeolite component being from 1:25 to 20:1.
U.S. patent application Ser. No. 08/096,873 concerns an improved process for preparing methyl tertiary butyl ether (MTBE) along with isobutylene and, optionally diisobutylene in one step by the reaction of tertiary butanol and methanol in the presence of a catalyst comprising .beta.-zeolite or .beta.-zeolite modified with a metal selected from the group consisting of Groups VB, VIIB, and VIII of the Periodic Table.
U.S. patent application Ser. No. 08/057,373 concerns an improved process for preparing ethyl tertiary butyl ether (ETBE) in one step by reaction of tertiary butanol and ethanol in the presence of .beta.-zeolite modified with Groups IB, VB, VIB, VIIB and VIII.
U.S. patent application Ser. No. 08/148,248 concerns the use of a palladium/platinum modified .beta.-zeolite for the one-step synthesis of methyl tertiary butyl ether (MTBE).
A number of U.S. patents, and allowed U.S. applications, and applications assigned to Texaco Chemical Co. disclose methods of making alkyl tertiary alkyl ethers, including MTBE and ETBE, in one step, from tert-butanol rather than isobutylene.
These include:
U.S. Pat. Nos.
4,822,921 PA1 4,827,048 PA1 5,099,072 PA1 5,081,318 PA1 5,059,725 PA1 5,157,162 PA1 5,162,592 PA1 5,157,161 PA1 5,183,947 PA1 07/917,218 PA1 07/878,121 PA1 07/917,885
and allowed U.S. Application Serial Nos.
Some of the limitations present in the MTBE catalyst systems generally available in the art include loss of activity at temperatures above 120.degree. C., deactivation due to the presence of peroxides and other organic components in the feedstock, lower than desirable selectivity and the requirement of multiple steps to accomplish the synthesis and separation of the product.
From the art available which is related to the synthesis of alkyl tertiary alkyl ethers it is apparent methods have become available in the recent past for one step synthesis from alcohols and butanol using various catalysts. However there is still a need for identifying catalysts which demonstrate improved catalyst life without sacrificing long-term productivity and good conversion levels.
It would represent a significant advance in the art tertiary butanol, instead of isobutylene and methanol could be reacted to form MTBE in one-step over a modified .beta.-zeolite catalyst which exhibits high levels of productivity and conversion for over 2000 hours of service.